This invention relates generally to packaging high voltage devices and more particularly concerns assembling an array of high voltage devices that are electrically isolated from one another on a lead frame that fits within conventional plastic packaging.
High voltage transistors have maximum voltage limitations. When a high voltage circuit is needed for a voltage greater than that sustainable by an individual high voltage transistor, several transistors are used to share the voltage between them. For instance, a circuit capable of sustaining 3000 volts may be made from a collection of transistors capable of each sustaining 1500 volts. This is done by having the substrates of some transistors at ground voltage and the substrates of some transistors at 1500 volts so that any one individual transistor only sees the 1500 volt drop it is capable of sustaining.
Packaging these high voltage transistors has been problematic because of the different substrate voltages needed. The substrates of the individual transistors must be kept electrically isolated from each other so that each transistor can maintain its appropriate voltage drop over the correct range of voltages. Current single tab lead frame designs do not provide the necessary electrical isolation of the substrates of the transistors, therefore the only way to accomplish this has been to package each transistor separately and then mount and connect the packages on a circuit board. This requires a great deal of board space. If a lead frame were available that provided electrical isolation of the substrates of two or more transistors then multiple transistors could be mounted together in a single package saving considerable board space and complexity.
Accordingly, it is the primary aim of the invention to provide a single lead frame that will allow for the mounting of two or more transistors with electrically isolated substrates within a single package.